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Solar Energy

June 30, 2008

Every month I get a unique feeling - and not the kind I enjoy. It’s similar to the feeling you get when you see blue flashing lights behind your car while driving. It’s that sudden "Oh... No..." sinking feeling produced by knowing you are completely helpless. I get this feeling every time I open my electric bill and I’m sure I’m not alone - especially these days. Oil and natural gas have both had major increases in cost. This makes me think,"how long before my electricity cost doubles?"

So, each month I look around the house wondering what I can do to be more efficient and realize that I’ve already trimmed to the point of discomfort. Surely there is an answer to the rising cost of energy? A few months ago I was repeating this exercise and walked outside to clear my mind. As I stood in the sun (in Florida) and began to get uncomfortably hot, I realized how much power was raining down on my house. Maybe I could improve the insulation or install an attic fan? "If only I could turn my entire roof into a solar panel for free", I thought. I’d need a bunch of panels since the efficiency of even the best photovoltaic cells are only around 20 to 23 percent.

Since I’m involved with energy efficiency matters at National Semiconductor, I often day dream about complete energy independence. There are many issues with disconnecting your home or office from the grid. Cost is the first and efficiency is the second. To power an average home, you’d need a large number of panels due to today’s solar conversion efficiencies. For example, assuming an average US household uses 900 kW-hrs per month and receives 10 hours of sunlight a day, you’d need panels that average an output of 3 kilowatts. The energy could be stored in batteries for times when there is no sun, or the home could remain connected to the grid and use that as storage for the excess electricity generated.

With this estimate, I had to ask the question, "Once you have enough panels for a 3 kilowatt output, will you always get 3 kilowatts?" The answer is, "probably not". Systems are usually deployed with the panels arranged in strings to increase the voltage, and the "strings" connected in parallel (see drawing 1) to increase the current. Think of them as batteries - when you want a higher voltage, you connect them in series. When you want more current, you connect them in parallel - the solar industry does the exact same thing. But what happens if one of your "batteries" or solar panels goes dead in the series string - depending on the failure, the string can go dead or lose voltage just like a string of batteries.

So, solar power panels suffer the same fate! If something as simple as the shade from an adjacent building or even bird droppings fall on a single panel, the entire string of panels can be affected. So my residential installation now needs to be a 6 kilowatt system to make sure this doesn’t happen - even less cost effective than my initial estimate. But what if you could fix the series issue with the panels and increase the overall efficiency of the string? Well, National Semiconductor has entered into the photovoltaic business with just such a solution. It is called SolarMagic™ and this technology solves the issue of variable output from each panel greatly improving the efficiency of the array.

There is even a cool video on solar powered golf carts - one with SolarMagic technology and the other without it - guess who wins? While I’m waiting for my own photovoltaic system to be installed (one day...), I’ll continue my efforts at reducing my own consumption and keep that sinking feeling each month to a minimum. Got comments on solar energy harvesting? Then drop me a comment or an email. Till next time...